The effect of duplex plasma nitriding-oxidizing treatment on the corrosion resistance of AISI 4130 steel

Plasma nitriding is a surface treatment process, which is widely used to improve wear, fatigue and corrosion resistance of the industrial parts. Nevertheless, corrosion resistance can be enhanced by oxidizing of the nitrided components. This paper considers the duplex treatment of plasma nitriding and post-oxidizing of AISI 4130 low alloy steel. After plasma nitriding, the post-oxidizing treatment was done in the various gas mixtures of O2/H2 and temperatures. The treated samples were characterized using metallographic techniques, XRD, SEM, micro-hardness and potentiodynamic test. The X-ray diffraction confirmed the development of gamma prime and epsilon iron nitride phases during the nitriding, and hematite (Fe2O3) and magnetite (Fe3O4) phases under the oxidizing process. The sample oxidized under O2/H2 volume ratio of 1/3 showed the best corrosion resistance, which is attributed to the formation of an almost single phase magnetite oxide layer on the top of the compound layer.